The present invention relates to a laser imaging apparatus which emits a modulated scanning beam to form an image pattern on a surface.
Conventionally, a laser imaging apparatus such as a direct imager of a laser photo plotter has been used for forming a circuit pattern or the like when a printed circuit board or a semiconductor element is manufactured. In such a laser imaging apparatus, a gas laser is typically employed as a laser source. The emitted laser beam is introduced into a modulator using a relaying optical system or the like. The modulator ON/OFF modulates the incident laser beam. Then, the modulated laser beam is deflected, by a deflector such as a polygonal mirror having a plurality of deflecting surfaces, thereby scanning the beam within a predetermined angular range. The deflected (i.e., scanning) laser beam is incident on an imaging optical system, such as an fxcex8 lens, which converges the beam on a photoconductive surface to form a scanning beam spot thereon so that a circuit pattern or the like is formed without a mask.
In such an imaging device, due to the deterioration of the sealed gas, the laser source should be exchanged. When the laser source is exchanged, the position and orientation of the laser beam are precisely adjusted so that the newly implemented laser source emits a beam precisely along the optical axis of the optical system.
Conventionally, in order to adjust the position and orientation of the laser beam, a plurality of targets, such as plates respectively formed with pinholes are provided in a light passage. Further, beam benders are provided, and the alignment of the laser beam with respect to the optical axis is achieved by adjusting the orientation of each of the beam benders so that the laser beam passes through each of the pinholes.
Each of the pinholes, however, is formed to have a relatively large diameter with respect to the diameter of the laser beam passes therethrough so that not only the center but also the peripheral portion of the Gaussian distribution thereof passes therethrough when the apparatus is used for forming the image. Therefore, in such a conventional alignment mechanism, alignment cannot be done at high precision.
Further, the alignment operation using the pinholes generally takes relatively long time, since the angle of each of the beam benders should be adjusted with confirming the position of the beam using a sensor or a fluorescing plate which may be located in the vicinity of every target position. Furthermore, the beam benders have too much degree of freedom in their changeable angles, which causes the adjustment operation to take longer period since the combination of the angles of the beam benders should be appropriately selected.
As the alignment of the laser beam with respect to the optical axis is required each time when the laser source is exchanged, there has been a demand for an apparatus with which the adjustment can be performed easily.
It is therefore an object of the invention to provide an improved laser imaging apparatus with which the alignment of the laser beam with respect to the optical axis can be done relatively easily at high accuracy.
For the above object, according to the present invention, there is provided a laser imaging apparatus which is provided with a laser source that emits a laser beam, a relaying optical system including a plurality of lens elements, the relaying optical systems relaying the laser beam emitted by the laser source, a deflector having at least one deflecting surface that deflects the laser beam relayed by the relaying optical system, an imaging optical system that converges the laser beam deflected by the at least one deflecting surface to form a beam spot on a surface to be scanned, an optical axis of the relaying optical system and an optical axis of the imaging optical system intersecting at a deflection reference point which is located in the vicinity of the at least one deflecting surface. The laser imaging apparatus is further provided with a first adjusting system that compensates for an inclination error of the laser beam incident on the at least one deflecting surface, the first adjusting system being provided in the relaying optical system, and a second adjusting system that compensates for a positional error of the laser beam incident on the at least one deflecting surface. The second adjusting system is provided in the relaying optical system.
With this configuration, the inclination and deviation of the laser beam with respect to the optical axis can be adjusted independently from each other, and thus can be adjusted relatively easily.
Optionally, a rear focal point of the relaying optical system may coincide with the deflection reference point, and a rear focal point of the imaging optical system may be on the surface to be scanned.
Further optionally, a beam emitting point of the laser source may be located on a front focal point of the relaying optical system.
Still optionally, the first adjusting system may include an optical system which deflects the laser beam at a point, within the relaying optical system, which is conjugate with the deflection reference point, a deflection direction being adjustable.
In a particular case, the first adjusting system may include an optical system which deviates the laser beam at a point, within the relaying optical system, which is conjugate with the rear focal point of the imaging optical system or in the close vicinity thereof, a deviation amount being adjustable.
Yet optionally, the laser imaging apparatus may include a beam position detector that detects an inclination error of a principal ray of the laser beam incident on the at least one deflection surface, with respect to the optical axis of the relaying optical system. The beam position detector may be located at one of a position conjugate with the rear focal point of the imaging optical system and in the vicinity thereof, and a position equivalent to the rear focal point of the imaging optical system and in the vicinity thereof.
In particular, the beam position detector may be located on a downstream side of the first adjusting system.
The laser imaging apparatus may further include a splitting member that splits the laser beam. The splitting member may be located at a position, within the relaying optical system, conjugate with the deflection reference position or in the vicinity thereof, a relaying lens, the relaying lens being arranged such that a front focal point thereof coincides with a rear focal point of an optical system located on an upstream side of the splitting member, and a beam position detector that receives the laser beam split by the splitting member and passed through the relaying lens, the beam position detector detecting a position at which the laser beam enters.
In this case, the splitting member is located on a rear side of the first adjusting system.
The second adjusting system includes an optical system that deflects the laser beam at a position, within the relaying optical system, which is conjugate with the rear focal point of the imaging optical system, a deflection direction being adjustable.
In an embodiment, the second adjusting system includes an optical system which deviates the laser beam at a point, within the relaying optical system, which is conjugate with the rear focal point of the imaging optical system or in the close vicinity thereof, a deviation amount being adjustable.
Further, the laser imaging apparatus may include a beam position detector that detects a positional error of a principal ray of the laser beam incident on the at least one deflection surface with respect to the optical axis of the relaying optical system as a deviation from the optical axis of the relaying optical system, the beam position detector being located at one of a position conjugate with the rear focal point of the imaging optical system and in the vicinity thereof, and a position equivalent to the rear focal point of the imaging optical system and in the vicinity thereof.
In this case, the beam position detector may be located on a downstream side of the second adjusting system.
The laser imaging apparatus may include a splitting member that splits the laser beam, the splitting member being located at a position, within the relaying optical system, conjugate with the rear focal point of the imaging optical system or in the vicinity thereof a relaying lens, the relaying lens being arranged such that a front focal point thereof coincides with a rear focal point of an optical system located on an upstream side of the splitting member, and a beam position detector that receives the laser beam split by the splitting member and passed through the relaying lens, the beam position detector detecting a position at which the laser beam enters.
Further, the splitting member may be located on a rear side of the second adjusting system.
Optionally, the relaying optical system may include a modulator that ON/OFF modulates the laser beam passing therethrough, and wherein the first and second adjusting systems are located on the front side of the modulator.
In such a case, the relaying optical system may include a collimating lens that collimates the laser beam emitted from the modulator.
Still optionally, the relaying optical system may include at least one reducing optical system that reduces a diameter of the laser beam.
According to another aspect of the invention, there is provided a laser imaging apparatus which is provided with a laser source that emits a laser beam, a relaying optical system including a plurality of lens elements, the relaying optical systems relaying the laser beam emitted by the laser source, a deflector that deflects the laser beam emitted by the laser source and relayed by the relaying optical system to scan, an imaging optical system that converges the laser beam deflected by the deflector to form a scanning beam spot on a surface to be scanned, a first adjusting system that compensates for an inclination error of the laser beam incident on the deflector, the first adjusting system being provided in the relaying optical system, and a second adjusting system that compensates for a positional error of the laser beam incident on the deflector, the second adjusting system being provided in the relaying optical system. In this case, compensation of the first adjusting system and compensation of the second adjusting system do not affect to each other.